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Class Myxini Order Myxiniformes Family Myxinidae (Hagfishes)

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Class Myxini Order Myxiniformes Family Myxinidae (Hagfishes) Class Myxini Order Myxiniformes Family Myxinidae (hagfishes) • Lacks jaws • Mouth not disk-like • barbels present • Unpaired fins as continuous fin-fold • Branchial skeleton not well developed • Eyes degenerate • 70-200 slime glands • Isoosmotic, simple kidneys, stenohayline, marine • Four rudimentary hearts • No true stomach • Unpaired gonads 1 Class Myxini Order Myxiniformes Family Myxinidae (hagfishes) • Knot-tying behavior • Scavengers • Rely heavily on cutaneous respiration • Global, deep sea distribution • Commercial interest – eelskin Class Petromyzontida Order Petromyzontiformes Family Petromyzontidae (Northern Lampreys) • 8 genera, 34 species • Dorsal fins continuous in adults • Oral disc • 7 pairs of gill openings • Single nostril • Pineal body opening • No bone • No scales • No paired fins • No jaws 2 Class Petromyzontida Order Petromyzontiformes Family Petromyzontidae (Northern Lampreys) • Anadramous and freshwater – Non-parasitic forms often freshwater – Parasitic forms often anadramous • Life history Class Petromyzontida Order Petromyzontiformes Family Petromyzontidae (Northern Lampreys) • Ammocoete • Parasitic forms: • Non-parasitic: 3 Class Conodonta, Conodonts • Extinct, late Triassic • First “teeth” • Cranium and teeth • No jaws • Small, thought to be of paedomorphic origin Class Pteraspidiomorphi • Extinct • One of the earliest known vertebrates • No jaws • Dermal skeleton • Little known, an extinct monophyletic lineage. 4 Class Anapsid • Extinct, Silurian period • 6-15 external branchial openings • Reduced or lost anal fin • Short paired fins • Series of large dorsal scutes • Hypocercal tail • No jaws • No massive head shield Class Cephalaspidomorphi, osteostraci • Extinct, early Silurian • No jaws • 10 pairs external gill openings • Dorsal eyes • Pectoral fins (homology to gnathostome pectoral fins not known) • Dorsal scutes reduced or lost 5 Gnathostomata • Monophyletic (including tetrapods) – Jaws derived from modified gill arches – Three semicircular canals in inner ear – Paired fins (usually) – Gill openings through slits (in fishes) – Dermal exoskeleton absent (usually) Class Placodermi • Extinct • Jaws, no teeth • Head and trunk shield • Braincase without nasal capsules • Jaw muscle not external to mandibular arch • Head and shoulder with dermal plates 6 Class Chodrichthyes – cartilagenous fishes • Dermal skeleton • Endoskeleton mostly cartilage • Jaws – Upper jaw – – Lower jaw – – teeth • No lung or swim bladder • Urea retention • Spiral valve • Pectoral fins with keratin based spine • Paired nares • Spiracle • Reproduction – Internal fertilization – – gestation period – No parental care – Large egg cases, no larval stage 7 Class Chondrichthyes, subclass Elasmobranchii, Order Lamniformes, mackerel sharks • Seven families, 10 genera, 15 species • 2 dorsal fins • Five gill slits • No nictitating membrane • No barbels • Spriacle behind eye • Examples Class Chondrichthyes, subclass Elasmobranchii, Order Carcharhiniformes, ground sharks • Eight families, 49 genera, 270+ species • 2 dorsal fins, no spines • Five gill slits, last 1-3 over pectoral fin • No gill rakers • Nictitating membrane • May have barbels or labial furrows • Spriacle usually absent • Mouth extends beyond eye • Oviparaous, ovoviviparous or viviparous • Examples 8 Class Chondrichthyes, subclass Elasmobranchii, Order Rajiformes, skates • Three families, >25 genera, >275 species • Snout pointed • Pectoral disc usually rhomboid • Thorns along midline of back • Caudal fin moderately well developed, without barb, may have two dorsal fins • Some electrogenic organs in tails • Males with enlarged spines near eyes • Oviparous Class Chondrichthyes, subclass Elasmobranchii, Order Myliobatiformes, stingrays • 33 genera, 178 species • 4-5 pairs of gill slits • Caudal fin and single dorsal fin reduced or absent • Sting from modified dermal denticle sheathed in venomous tissue • Pectoral disc rounded, oval or triangular • No thorns along midline • Ovoviviparous 9 Class Chondrichthyes, subclass Elasmobranchii, Order Myliobatiformes, stingrays • Taxononomy recently revised, skates and rays were previously grouped together • Freshwater or marine Class Chondrichthyes, subclass Holocephali, Family Chimeridae • 3 families, 6 genera, 33 species • Global distribution, marine only • 1 external gill opening, 4 covered by soft operculum • two dorsal fins, first with venomous spine • teeth • large pectoral fins with fleshy base • elongate tail • Oviparous, • Upper jaw fused to cranium 10.
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